Gas cloud 20 times bigger than the Milky Way may have been left by a cosmic intruder, study...

Scientists have discovered a gigantic trail of gas drifting out from a quintet of warring galaxies. The mysterious gas cloud — the largest ever seen around a group of galaxies — may have been left behind by a “cosmic intruder,” a new study reveals. The cloud — an unexplained, 2 million light-year-wide stream of hydrogen gas coming from the galactic group known as Stephan's Quintet — was discovered by the deepest ever scan of the region by the Five-hundred-meter Aperture Spherical Telescope (FAST) in China. Researchers think the gas trail,, could be "tidal debris" formed after the whirling galaxies collided with a large cosmic intruder roughly 1 billion years ago.